It seems that Rowling did some research regarding Western Occultism for her novels but the material is used to help create texture and advance a fictional story about a magical universe and not to accurately portray the demimonde of Western Occultism or act as a primer for it. That she took this step shows that she is a good writer not necessarily an occultist. A fantasy fiction series I am working on (for adults) also contains a lot of information that refers to Western occultism and Eastern and Western mysticism because I have background in these things, but the books are meant for insight and entertainment, not to indoctrinate someone into a belief or practice.
In real Western Occultism, men and women identify as mages or sorcerers (not wizards or witches). In modern Western folk magic tradition, men and women both identify as witches (not as wizards and witches--but no one who practiced folk magic before about the late 19th century called him or herself a "witch." Such people were called cunning folk, or wise man/woman, a fixer, healer, or else a mage or sorcerer/sorceress).
Avada Kedavra is a variation of "Abracadabra," which was written in a magic square and thought to have magical healing powers. Magical squares and anagrams were very popular during the medieval times (among Christians) and probably got their start in games similar to Sodoku that were popular among the ancient Romans.
Western Occultism and Paganism are 2 different things. Pagan (pre-Christian cultures, that is) were just as squeamish about magic as the Christian culture actually. A lot of Western Occultism, however, emerged as an alternative expression of medieval Hermetic Christianity. Who preserved, compiled, and even wrote many of the medieval grimoire (magical books) we have access to? clerics within the Christian Church, that's who.
So, please, enjoy your Harry Potter books. It is a great fantasy series for young adults about friendship and heroism and righting wrongs that will go down in history as a major classic.